A rabbit anti-human bladder cancer tissue antibody (RABCa) was prepared and was reacted against urine samples from a series of cancerous and non-cancerous patients by both micro-complement fixation and Ouchterlony gel diffusion. RABCa vs. urine from cancer patients showed a peak CF to 1 g of total protein vs. only 3 g with non-bladder cancer urines. When RABCa was reacted in agar gels against membrane antigenic extracts of bladder cancers and normal patients, a separate precipitation band of identity was visible against 66.7% of the cancer specimens (urines) and in only 3.2% of normal urines. Non-cancer bands could be removed by absorption with either normal bladder tissue or urine. Gel fractionation (Sephadex G-l00 and G-200) of urines suggests that RABCa reacts in the CF and Ouchterlony assays with a component or urine which has a molecular weight greater than 100,000. A rabbit antisera to this active fraction has lead to the identification of both heat labile (70 degrees C - 30 min) and heat stable cancer associated antigens. Further purification studies and assays have shown the heat labile fraction to be an immunoglobulin like molecule. Anti-immunoglobulin sera (IgG) in fact have shown precipitin bands in gel diffusion vs. 60% of cancer urines. The heat stable bands have been resolved into at least two components which can be separated Sephadex G-100 chromatography. Studies in progress involve the production of an antisera to the heat stable component and further identification of specific bladder cancer associated antigens.